From: jim bell <jimbell@pacifier.com>
Date: Mon, 30 Sep 1996 05:35:04 +0800
To: tcmay@buckeye.got.net
Subject: Re: GPS and other Dual-use technologies
Message-ID: <199609291915.MAA04736@mail.pacifier.com>
MIME-Version: 1.0
Content-Type: text/plain


At 10:34 AM 9/29/96 -0700, Steve Schear wrote:
>I used to be an avid RC modeler and have contemplated organizing an
>on-going amateur cruise missile contest.  The object would be to accurately
>deliver various payload weights over courses of various terrain and
>distances (perhaps out to a hundred miles or more in the case of Giant
>Scale craft).  Judging would be based on speed, stealth (noise, IR
>emissions and radar cross section) and accuracy.
>
>Craft are free to use any navigational technology, but must be autonomous
>from launch to delivery.  To aid navigation I was considering the design of
>a substitute differential GPS beacon functionally interchangable with those
>offered by the USCG.  My device would work on a different frequency,
>possibly using very wideband direct sequence spread spectrum (for low
>probability of intercept/detection) and be actuated by the missile as it
>neared the target in order to refine its position.

The data standard for differential corrections is called "RTCM-104", and 
it's the signal you input into differential-capable GPS receivers.  Boxes to 
generate RTCM-104 are probably relatively cheap, primarily needing a 
multi-channel GPS receiver and another processor for coding.  Differential 
corrections can, of course, be transmitted on any frequency you'd like, 
including frequency-hopping if you're really concerned about intercept.  
(which you won't be...)

Incidentally, GPS receivers are getting REALLY small these days, 
particularly for just the module-level products.  A size like about 1 inch 
by 2-inches is pretty close to state-of-the-art.  Power consumption is about 
3/4 watt.


Jim Bell
jimbell@pacifier.com